My calla lilies don’t bloom
They have white on their leaves. They were given to me by a neighbor. I store them under my house, just like she does and bring them out in spring.
Certified GKH Gardening Expert
This could be powdery mildew from being stored in a damp location.
Treat the plant with Neem Oil.
They also may need more Phosphorous to encourage flowering. Bone Meal is a good way to do so.
Here are some links that will help.